How to convert files to Base64 in React

Question

I have registration for in React where I need to upload files to the server. Those files needs to be Base64 encoded.

The function to encode it is as follows:

getBase64(file) {
        let document = "";
        let reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload = function () {
            document = reader.result;
        };
        reader.onerror = function (error) {
            console.log('Error: ', error);
        };

        return document;
    }

And function to handle click on form's next button is as follow:

handleNextButtonClick(event){
    event.preventDefault();
    let data = {domainId: this.props.user[0].domainId, name: steps.stepThree, values: this.state.files};

    let idCard = this.state.files.filter(file => file.file_type === "ID_CARD")[0].values.file;
    let statuses = this.state.files.filter(file => file.file_type === "STATUTES")[0].values.file;
    let blankLetterHead = this.state.files.filter(file => file.file_type === "LETTER_HEAD")[0].values.file;
    let companyPhoto = this.state.files.filter(file => file.file_type === "COMPANY_PICTURE")[0].values.file;


    let idCardBase64 = this.getBase64(idCard);
    let statusesBase64 = this.getBase64(statuses);
    let blankLetterHeadBase64 = this.getBase64(blankLetterHead);
    let companyPhotoBase64 = this.getBase64(companyPhoto);
}

If I console log for example the first one this.state.files.filter(file => file.file_type === "ID_CARD")[0].values.file; I get

Everything seems ok, but I'm getting error:

Uncaught TypeError: Failed to execute 'readAsDataURL' on 'FileReader': parameter 1 is not of type 'Blob'.

Any idea how to solve this?

UPDATE

let idCardBase64 = idCard ? this.getBase64(idCard) : "";
let statusesBase64 = statuses ? this.getBase64(statuses) : "";
let blankLetterHeadBase64 = blankLetterHead ? this.getBase64(blankLetterHead) : "";
let companyPhotoBase64 = companyPhoto ? this.getBase64(companyPhoto) : "";

I changed it. And in this case exists only idCard. Now I do not get any errors but idCardBase64 is "" and not Base64 encoded.

Answer 1

file reading is asynchronous. so use callback or promise to solve your problem.

let idCardBase64 = '';
this.getBase64(idCard, (result) => {
     idCardBase64 = result;
});

and use callback to return the data which you get.

getBase64(file, cb) {
    let reader = new FileReader();
    reader.readAsDataURL(file);
    reader.onload = function () {
        cb(reader.result)
    };
    reader.onerror = function (error) {
        console.log('Error: ', error);
    };
}